1. Field of the Invention
The present invention relates to a rolling bearing system.
2. Description of the Related Art
Generally, it is known that the service life of a rolling bearing involves a life depending on a metal fatigue of each component, caused by a load applied to rolling elements and raceway surfaces of bearing rings (so called “a rolling contact fatigue life”), and a life depending on a degradation of a grease used to provide a lubricating oil film between the rolling elements and the raceway surfaces (so called “a grease life”). The rolling contact fatigue life tends to be improved with the recent improvement of the cleanliness of bearing materials. As for the grease life, however, the grease confined between the bearing rings (i.e., an inner ring and an outer ring) usually cannot contribute to improve the lubricity of portions of components, other than portions contacting with the surface of the rolling elements and the raceway surface as well as portions near the contacting portions. Therefore, the grease is generally liable to be easily degraded, and the resultant lubrication failure constitutes a main factor determining the service life of the bearing.
Conventionally, in order to improve the grease life, measures have been taken such that new grease is supplied from a source external to the bearing. However, in these measures, the grease is generally supplied to the bearing through a tube from an external grease source, which may complicate a grease supply passage. Also, a certain post-machining is required to form a grease pouring hole in the bearing ring (e.g., the outer ring) or to form a grease supply channel in a housing onto which the bearing ring (e.g., the outer ring) is secured.
On the other hand, a configuration in which a lubricant storage section is provided inside the bearing has been conventionally proposed. For example, Japanese Utility Model No. 2540977 (JP-Y2-2540977) discloses a double-row type rolling bearing including an inner ring spacer defining a lubricant storage space. The inner ring spacer is arranged between a pair of inner rings, and includes an inner peripheral part and an outer peripheral part fitted to the inner peripheral part. The lubricant storage space for storing a lubricant is formed between the inner and outer peripheral parts. A minute lubricant outflow passage is formed on a fitting interface between the inner and outer peripheral parts of the inner ring spacer, so as to extend from the lubricant storage space to open toward the neighborhood of the raceway surface of the inner ring.
Also, Japanese Utility Model No. 2518950 (JP-Y2-2518950) discloses a double-row type rolling bearing including an inner ring spacer defining a lubricant storage space. The inner ring spacer is provided with an annular groove for holding the lubricant, along the inner peripheral surface adapted to be fitted to a shaft. Also, the inner ring space is provided with a pair of through holes opening in opposite axial-end surfaces thereof and formed to communicate with the annular groove. These through holes act as lubricant supply passages and open toward the neighborhood of the raceway surfaces of the pair of inner rings.
Further, Japanese Unexamined Utility Model Publication (Kokai) No. 5-92538 (JP-U-5-92538) discloses a roller bearing in which a rolling element (or a roller) has a hollow structure and a lubricant is filled in the interior space of the rolling element. A cap is attached to an opening of the internal space, which is formed in an axial end face of the hollow roller. A minute gap is defined in a fitting interface between the roller opening and the cap, so as to form a lubricant outflow passage.
The above-described conventional structures, in which a lubricant storage section is incorporated inside a bearing, require a machining or other process for forming a space for holding a lubricant in an inner ring spacer or a rolling element (or a roller).